Diagram Chase in Relational System Development

We propose diagrammatic techniques for visualizing relational reasoning in formal methods like B or Z; in particular for induction and coinduction. These are similar to those for functional diagrams in category theory and inspired by rewriting theory. Diagrams are endowed with a simple algebraic semantics that imposes a convenient balance between expressive and algorithmic power. This makes the approach particularly suitable for mechanization and automation. Its usefulness for visual reasoning is illustrated by various examples.